MFC r357940 (by mjg), r365932 (by jrtc27):
Make atomic_load_ptr type-aware
atomic_common.h: Fix the volatile qualifier placement in atomic_load_ptr

(cherry picked from commit 082a6b2a92888cf799c7a0408a78e2d7ad9320bb)
(cherry picked from commit 7d54cc9165a3990849b60835c85ddb388905e1b7)